Caloric restriction has been shown to extend the mean and maximal lifespan and slow the aging rate in a number of lower species, primarily mice and rats. In particular, the increase in maximal lifespan in mice and rats appears to depend primary on caloric restriction (CR) which is associated with later appearances and lowered incidence of most naturally occurring diseases. The mechanisms by which CR exerts its anti-aging effect are unknown. Recently, it was observed in a lower species that life-span regulation and increased longevity by insulin-like metabolic control is analogous to mammalian longevity enhancement induced by caloric restriction. Therefore, in light of the interest in mechanisms of action of CR, physiological validity, and possible application for human subjects, it has become essential to test caloric restriction in animal models that more closely resemble humans, particularly for age associated disease. Such is the aims of our non-human primate trail (e.g. Parent Trial) evaluating the effect of caloric restriction on an age associated disease (i.e. atherosclerosis). The hypothesis for the Parent Trial is that caloric restriction over an sustained period when compared to an ad lib diet, may delay the onset of atherosclerosis by reducing age associated increases in glycated products, reducing intra-abdominal fat, and improving insulin sensitivity. It is the improved insulin sensitivity that is noted as a consistent metabolic feature secondary to prolonged CR not only in rodent studies, but in on going trials assessing CR in higher species such as non-human primates including our Parent trial. The specific focus of this application is to evaluate potential cellular mechanisms by which caloric restrition may improve insulin action in vivo. Our working hypothesis is that signal transduction through insulin receptors is diminished with aging is improved secondary to crhonic CR. Our specific hypothesis is that caloric restriction improves insulin sensitivity by enhancing insulin receptor signal transduction. Specifically, we propoose CR improves insulin action by 1)enhancing insulin receptor substrate (IRS) phosphorylation and 3) enhancing IRS association with cytosolic substrates known to be involved with in vivo insulin action. Our specific aims to evaluate the mechanistic basis behind the enhanced insulin sensitivity inducecd by CR will be tested in tissues collected as part of a non-human primate caloric restriciton trial. These tissues have been processed and stored appropriately after both basal and in vivo insulin stimulated conditions and specific cellular signaling will be asessed The focus on cellular mechanisms by which CR may improve insulin sensitivity in higher species combined with the clinical and metabolic measuremetns obtained as part of a completed Parent Trial will provide a comprehnsive evaluation of how CR may alter glucose metabolism with age and is unique feature of this revised submission.